Surgical Technique

When the patient is in the operating room and has been placed prone on a fluoroscopic table, the back is prepped and draped in a sterile fashion. The area is squared off with sterile towels and a large-opening "chest-breast" drape is applied. The wide exposure enables placement of the catheter and tunneling to the side. A 1 to 2 in. incision is made inferior to the desired intrathecal entry point of the Tuohy needle, and a paraspinous intrathecal puncture is performed under flu-oroscopic guidance. The catheter is then introduced to the desired target level under fluoroscopic guidance, most often at the T10 level but locations may be selected according to the pathology or placement of the pain generator. A second "extension" catheter, which is disposable, is tunneled to the flank by means of a malleable catheter passer.

This catheter is then connected to the intrathecal catheter with a suitable connector, tied with a 2-0 silk suture, and then anchored to the lumbar fascia with another 2-0 silk suture in a figure-of-8 configuration. The wound is closed with an interrupted inverted stitch of 3-0 ab-sorbable material, and Steri-Strips are applied to the skin edge. Alternatively, staples may be used. An antiseptic bandage is placed around the percutaneously exiting catheter. A Biopatch (Johnson & Johnson) impregnated with chlorhexidine gluconate (Hibiclens) is used in the author's clinic. Some external extension catheters require fitting a Luer-Lok adapter on the externalized catheter to facilitate mating with the infusion catheter coming from the external pump. The back wound is dressed, and the patient is now ready to begin receiving medication for the screening trial.

Management of the patient's opioid use at the time of screening is important. Eliminating opioids before screening may lead to unwarranted discomfort to the patient and may add to the expense of the trial.25 A complete conversion from systemic opioid to intraspinal opi-oid may result in an abstinence syndrome. Therefore a clinical protocol during the screening trial is necessary to prevent withdrawal side effects. One such protocol, suggested by Krames, involves converting 50% of the pretrial oral dose to an intrathecal equivalent dose and withdrawing the remaining oral dose by 20% per day, converting to an equianalgesic intrathecal dose. The dose may then be increased to an intrathecal effect while the systemic medication is decreased.31

For the tunneled catheter trial, the patient is usually kept in the hospital for 3 days, although some clinicians are beginning to utilize outpatient trials of 1 week or longer. The length of trial may be an important consideration. Presumably, the longer a trial proceeds, the less likely it is that a placebo response will affect the outcome. Many clinicians believe that a longer trial better predicts a successful outcome.

If the screening trial is successful, the patient generally reports a 50% decrease in pain as measured by some standardized self-reporting measure or Visual Analog Scale (VAS) and reports no intolerable side effects. The patient then proceeds to implantation of the chosen drug administration system.

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